1. Field of the Invention
Embodiments of the present invention relate, in general, to resource sharing in wireless networks and more particularly to resource sharing in a personal independent basic service set cluster.
2. Relevant Background
Within wireless communication systems, a wireless communication device is normally referred to as a station or STA (e.g., a wireless station). Examples of wireless stations (STAs) include a wide variety of wireless communication devices (e.g., computers including laptop computers, PDAs, cell phones, etc.). In addition, various wireless communication systems can be configured to operate using different means of communication (e.g., ad hoc, peer to peer, etc.). The basic building block of a wireless network is a Basic Service Set (BSS). A BSS is a group of STAs that communicate with each other. Communications take place within the area surrounding these stations called a Basic Service Area (BSA). The BSA is defined by the propagation characteristics of the wireless medium.
An Independent BSS (IBSS) is one in which stations can communicate directly with each other and thus must be within direct communication range. Typically, IBSS networks are composed of small numbers of stations set up for a specific purpose or for a short period of time. One common use is to create a short-lived network to support a single meeting in a conference room. Due to the short duration, small size, and focused purpose, IBSSs are sometimes referred to as ad hoc BSS or an ad hoc network. Such small personalized type of ad hoc networks are also referred to as personal or private IBSS networks (PBSS).
In some wireless communication systems, a PBSS coordinator point (PCP) may operate as a central governing communication device to which and through which various other STAs within the wireless communication systems communicate. For example, the PCP may serve as a coordinator of various other STAs within the wireless communication system or BSS, and it may also serve as a gateway to another network (e.g., a wide area network (WAN), the Internet, etc.).
Access to the wireless medium through which the stations communicate is controlled by a coordination function. In a PBSS there are numerous ways to access the communication medium. These include a contention-based period or contention-based access, an isochronous service period or pseudo-static service period and asynchronous service period or a service period request/allocation per beacon interval.
A contention-based protocol (CBP) is a communications protocol for operating wireless telecommunication equipment that allows many users to use the same radio channel without pre-coordination. The “listen before talk” operating procedure in IEEE 802.11 is the most well known contention-based protocol. Using a contention based protocol multiple independent stations can interact without central control. Before attempting to transmit, each station checks whether the medium is idle. If the medium is not idle, stations defer to each other and employ an orderly exponential back-off algorithm to avoid collisions.
“Isochronous” literally means to occur at the same time or at equal time intervals. In general English language, it refers to something that occurs at a regular interval of the same duration, as opposed to synchronous which refers to more than one thing happening at the same time. The term is used in different technical contexts, but often refers to the primary subject maintaining a certain interval, despite variations in other measurable factors in the same system.
In telecommunication, isochronous is known to mean a periodic signal pertaining to transmission in which the time interval separating any two corresponding transitions is equal to the unit interval or to a multiple of the unit interval
When a transfer of information is “synchronous,” the sending and receiving devices are synchronized, such as by using the same clock signal, and the transfer of information re-occurs at identical periodic intervals. For example, the input/output (IO) device 10 can send a synchronous message, indicating the camera's current mode, to the computer system 100 once every second. However, because the IO device 10 and the computer system 100, or components within the computer system 100, may be difficult to synchronize, a synchronous transfer of information may not be appropriate in some situations.
When a transfer of information is “isochronous,” the sending and receiving devices are only partially synchronized, but the sending device transfers information to the receiving device at regular intervals. Such transfers can be used, for example, when information needs to arrive at the receiving device at the same rate it is sent from the sending device, but without precise synchronization of each individual data item. For example, an Input/Output device may send an isochronous stream of video information to the computer system which ensures that the information flows continuously, and at a steady rate, in close timing with the ability of the computer system to receive and display the video. While a synchronous transfer of information typically involves having each data transfer occur at the same time with respect to a clock signal, an isochronous transfer of information may require that up to “X” bits of data be transferred every “T” time units, although precisely when the X bits are transferred within the time T can vary.
In telecommunications, asynchronous communication is transmission of data without the use of an external clock signal. Any timing required to recover data from the communication symbols is encoded within the symbols. The most significant aspect of asynchronous communications is variable bit rate, or that the transmitter and receiver clock generators do not have to be exactly synchronized.
Each of the aforementioned techniques for access to the communication medium has advantages and disadvantages, both of which are amplified when PBSSs are clustered. PBSS clustering occurs when individual PBSS networks overlap. In such a situation interference mitigation of the overlapping networks is employed when each PBSS operates on the same channel. In such a situation the beacon intervals are aligned in the PBSS cluster. A spatial reuse mechanism is defined for fixed traffic mode (isochronous service period (SP)) in each PBSS.
FIG. 1 is a depiction of a spatial reuse mechanism for fixed traffic in a PBSS as would be known to one of ordinary skill in the relevant art. As shown three PBSS networks overlap in which each network includes two stations. Within each beacon interval each PBSS is given an offset time slot during which it may transmit. During this transmit period other PBSS networks within the PBSS cluster are prevented from transmission and relegated to a receive only mode.
It is not clear, however, how to allocate and share a beacon interval among overlapping PBSSs. Indeed a solution should harmonize all 3 kinds of time slot medium access techniques for data transmission: contention-based protocol, isochronous SP, and asynchronous SP. A need exists, therefore, for a method or protocol and associated system to define how to use a shared beacon interval among overlapping PBSS networks. These and other challenges of the prior art are addressed by one or more embodiments of the present invention.